Photoresponsive hexahydrotriazine polymers

ABSTRACT

This disclosure describes new compositions and methods related to photoresponsive poly(hexahydrotriazines) and related polymers. In an embodiment, a method of patterning a substrate includes forming a liquid poly(hemiaminal) material by a process that includes forming a reaction mixture comprising a polar solvent, paraformaldehyde, and an aminobenzene compound having photoreactive groups, and heating the reaction mixture at a temperature up to 50° C. The method further includes applying the liquid poly(hemiaminal) material to a substrate; patterning the liquid poly(hemiaminal) material with UV light; and curing the liquid poly(hemiaminal) material to form a cured poly(hexahydrotriazine) polymer.

This application is a divisional of co-pending U.S. patent applicationSer. No. 15/445,628, filed Feb. 28, 2017, which is a divisional ofco-pending U.S. patent application Ser. No. 15/016,610, filed Feb. 5,2016, now U.S. Pat. No. 9,828,467. The aforementioned related patentapplications are herein incorporated by reference in their entirety.

FIELD

The present disclosure relates to new compositions and methods relatedto polyhexahydrotriazines and related polymers. The compositions andmethods described herein are useful for removable and recyclablecoatings and for photoresists used in electronic applications.

BACKGROUND

Poly(hexahydrotriazine) polymers (PHTs) are an emerging class of highstrength engineering thermoset polymers that have a unique combinationof properties. They have high modulus, solvent resistance, andresistance to environmental stress cracking, yet they can be easilyrecycled by decomposition to monomers in a strong acid. PHTs may beobtained from heat treatment of a poly(hemiaminal) (PHA) polymer, whichmay be dissolved in a polar solvent. This enables the preparation of PHTfilms by solvent casting.

A new subset of PHAs and PHTs may be altered by ultraviolet (UV)irradiation of photoresponsive groups bonded to a PHA or a PHT polymerchain and/or a PHT polymer network. The photoresponsive groups engage inthe bonding and/or debonding of portions of the polymer and/or thegreater polymer network when exposed to UV light. Some of thesephoto-induced chemical reactions are referred to as photodimerisationreactions. Reactions of this type may proceed by either a [4π+4π] or[2π+2π] cycloaddition mechanism that can be reversed upon application ofan appropriate wavelength of light. In the case of the [2π+2π]cycloaddition reaction, photodimerisation occurs between two alkenes toform a cyclobutane dimer. Some examples of small molecules andphotodimerisation reactions are presented in FIG. 1, including therespective wavelengths of light that may be used in the photoreversiblereactions.

The new photoresponsive PHAs and PHTs presented herein uniquely providea rigid high modulus and chemically resistant thermoset polymer and thatmay be reversibly altered by UV irradiation. Processing of suchphotoresponsive polymers may be non-destructive and may be performed inlocalized areas of a polymer film to create patterns in the polymerfilm.

SUMMARY

Described herein is a polyhexahydrotriazine (PHT) with a plurality oftrivalent hexahydrotriazine groups having the structure

and a plurality of phenyl groups having the structure

and wherein each wavy bond site of a given hexahydrotriazine group iscovalently linked at a respective wavy bond site of a phenyl group, andeach wavy bond site of a given phenyl group is covalently linked at arespective wavy bond site of a hexahydrotriazine group, and wherein atleast one of A, B, C, D, and E is a photoreactive group. Additionally,at least one of A, B, C, D, or E is a bridging group between at leasttwo hexahydrotriazine groups. Additionally, least one of A, B, C, D, andE absorbs ultraviolet radiation, and at least one of A, B, C, D, and Ecomprises a reaction product of ultraviolet radiation absorption. Thereaction product is a product of a photoreversible reaction, such as acyclic carbon group, or a cycloaliphatic carbon group that is thereaction product of a [2π+2π] cycloaddition reaction or a [4π+4π]cycloaddition reaction. The cycloaliphatic carbon group may be acyclobutane group that is a photoreaction product of at least twocarbon-carbon double bonds that may be resonance stabilized. Furtherprovided is a PHT wherein at least one of A, B, C, D, and E comprises acarbon-carbon double bond, wherein at least one carbon-carbon doublebond is resonance stabilized and/or one conjugated carbon-carbon doublebond from a photo-cleavage reaction, such as a reaction product of acyclobutane photo-cleavage reaction.

In an embodiment, a method of patterning a substrate includes forming aliquid poly(hemiaminal) material by a process that includes forming areaction mixture comprising a polar solvent, paraformaldehyde, and anaminobenzene compound having photoreactive groups, and heating thereaction mixture at a temperature up to 50° C. The method furtherincludes applying the liquid poly(hemiaminal) material to a substrate;patterning the liquid poly(hemiaminal) material with UV light; andcuring the liquid poly(hemiaminal) material to form a curedpoly(hexahydrotriazine) polymer.

In another embodiment, a method of patterning a substrate includesforming a liquid poly(hemiaminal) material by a process that includesforming a reaction mixture comprising a polar solvent, paraformaldehyde,and an aminobenzene compound comprising photoreactive groups and atleast two amine groups; and heating the reaction mixture at atemperature up to 50° C. The method further includes applying the liquidpoly(hemiaminal) material to a substrate; patterning the liquidpoly(hemiaminal) material with UV light; and curing the liquidpoly(hemiaminal) material to form a cured poly(hexahydrotriazine)polymer.

In another embodiment, a method of patterning a substrate includesforming a liquid poly(hemiaminal) material by a process that includesforming a reaction mixture comprising a polar solvent, paraformaldehyde,and an aminobenzene compound comprising photoreactive groups, thephotoreactive group comprising a reaction product of a [2π+2π]cycloaddition reaction, a reverse [2π+2π] cycloaddition reaction, a[4π+4π] cycloaddition reaction, a reverse [4π+4πc] cycloadditionreaction, or a combination thereof; and heating the reaction mixture ata temperature up to 50° C. The method further includes applying theliquid poly(hemiaminal) material to a substrate; patterning the liquidpoly(hemiaminal) material with UV light; and curing the liquidpoly(hemiaminal) material to form a cured poly(hexahydrotriazine)polymer.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

So that the manner in which the above recited features of the presentdisclosure can be understood in detail, a more particular description ofthis disclosure, briefly summarized above, may be had by reference toembodiments, some of which are illustrated in the appended drawings andin the body of the specification. It is to be noted, however, that theappended and embedded drawings illustrate only typical embodiments ofthis disclosure and are therefore not to be considered limiting of itsscope, for the disclosure may admit to other equally effectiveembodiments.

FIG. 1 shows some examples of photoreactive small molecules andphotodimerisation reactions.

FIG. 2 is a series of UV-visible spectroscopy absorbance plots.

FIGS. 3A-3C show a substrate undergoing a photoresist process that usesa photoresponsive PHT.

To facilitate understanding, identical reference numerals have beenused, where possible, to designate identical elements that are common tothe figures and drawings. It is contemplated that elements disclosed inone embodiment may be beneficially utilized on other embodiments withoutspecific recitation.

DETAILED DESCRIPTION

Stimuli-responsive polymeric systems including photoresponsive polymers(PRPs) are used to fabricate smart functional materials for use in avariety of technological and consumer applications. Photoresponsivepolymers are useful due to their responses upon the application oflight, such as UV light, which may initiate and cause thenon-destructive bonding and debonding of chemical structures within apolymer network. Light activated chemical reactions of PRPs may beadvantageously performed with a PRP in the solid, glassy, rubbery, orliquid state, and at ambient temperatures. Construction ofphotoresponsive polymeric networks may be achieved using photoreversiblereactions such as photodimerisation.

Disclosed herein are new PHT polymers that combine the rigidity and highmodulus of thermoset polymers, with photoresponsive and photoreversiblechemical groups that allow the polymer to be structurally altered whenirradiated with UV light. In some embodiments of this disclosure, PHAsand PHTs may be structurally altered by photochemical modification inlocalized areas of the material using patterned mask(s), such as thoseused to create patterns in conventional photoresist materials. Usefulphotoresponsive groups chemically bonded to polymers containinghexahydrotriazine groups may be selected from those groups that undergobonding and debonding in the presence of UV light at certainwavelengths. These groups may include, but are not restricted toanthracene, cinnamic acid, coumarin, thymine, and stilbene groups, whichmay react by either a [4π+4π] or [2π+2π] cycloaddition mechanism. Such areaction may be reversed to reproduce the initial or starting chemicalgroups upon application of an appropriate wavelength of light. Reactionexample 1 illustrates one method for forming a photoresponsive PHT thatcontains conjugated carbon-carbon double bonds that may undergo [2π+2π]cycloaddition reactions:

Reaction Example 1

Reaction example 1 involves the use of the free base form of4,4′-diaminostilbene, which contains a photo-labile and resonancestabilized double bond and aminobenzene groups. We note that in thisdisclosure, aminobenzene, phenylamine, and aniline are the samecompound. Reference to “an aminobenzene”, “aminobenzenes”, and“aminobenzene compounds” does not only refer to the single compoundaminobenzene, but also includes all varieties of substitutedaminobenzenes, that are molecules useful in the synthesis of PHTmaterials. The hydrochloride salt of 4,4′-diaminostilbene used inreaction example 1, is available from Sigma-Aldrich Chemical Co, St.Louis, Mo., USA.

In one embodiment, a photoresponsive PHT, such as that exemplified inreaction example 1, may be produced as follows: a temperature controlledreaction vessel containing a magnetic stir bar and padded with drynitrogen may be charged with dry and degassed N-methylpyrrolidone (NMP)solvent (1.5 mL), 4,4′-diaminostilbene (1 mmol) and paraformaldehyde(0.1 g, 3.33 mmol). A useful ratio of aromatic amine to paraformaldehyde(PF) is approximately 0.5 mole aromatic amine:1.25 mole PF. Thecomponents may then be stirred at 50° C. until the solution is clear(˜15 minutes). This produces an intermediate poly(hemiaminal) (PHA)material that contains photoresponsive groups, such as resonancestabilized carbon-carbon double bonds, as illustrated in reactionexample 2.

Reaction Example 2

In one embodiment, a PHA material, such as that produced in reactionexample 2, may be applied to an electronic article using a techniquesuch as spin-coating or spray coating. After application of the PHAmaterial, the film or coating may be reacted with UV light, and then maybe converted to a PHT polymer upon further heating. In anotherembodiment, the photoresponsive polymer material may be a mixture of PHAand PHT polymers. In one embodiment, a photoresponsive PHA coating maybe converted to a high modulus photoresponsive PHT by depositing a PHAsolution on a glass microscope slide (with 80 μm thickness aluminum tapeboundaries) using a glass Pasteur pipette. The following thermaltreatment may then be used to drive off the solvent and transform thePHA film to a PHT film: 50° C. for 1 hour, 50° C. to 110° C. over 1hour, 110° C. for 1 hour, 110° C. to 200° C. over 1 hour, and then 200°C. for 1 hour, after which time the PHT film may be cooled to ˜23° C.The aluminum tape may then be peeled off the slide and a photoresponsivePHT film may be isolated by floatation from the glass slide by soakingin deionized water. In another embodiment, a photoresponsive PHT filmmay be well adhered to a quartz substrate and used directly inphotodimerisation experiments. We note that equipment other than thespecific equipment described in the embodiment may be used, and that thereaction may be performed at larger scales. Mechanical stirring or flowstirring may be used for mixing instead of a magnetic stirrer, and anysuitable process may be used to convert PHA to PHT so long as theprocessing temperatures are observed.

Photodimerisation or photoreaction of the photoresponsive PHT polymerproduced from reaction example 1 is illustrated by reaction example 3,wherein the photoresponsive PHT polymer from reaction example 1,containing resonance stabilized carbon-carbon double bonds, reacts withadjacent resonance stabilized carbon-carbon double bonds, to form aphotoresponsive PHT polymer containing cyclobutane groups:

Reaction Example 3

As shown in reaction example 3, dimerisation or reaction of thephotoresponsive PHT from reaction example 1 to form cyclobutane linksand groups may be achieved by irradiation of a photoresponsive PHT filmby UV light of a wavelength from about 300 nm to about 400 nm in a dryoxygen free environment. Recovery of the photoresponsive PHT containingresonance stabilized carbon-carbon double bonds may achieved byirradiation of the photoresponsive PHT film containing cyclobutanegroups with UV light of a wavelength from about 190 nm to about 250 nmin a dry oxygen free environment. Generally, a UV radiation at a radiantexposure level of between about 0.1 J/cm² and about 500 J/cm² for aperiod of time of between about 0.1 seconds and about 100 seconds may beused in the forward and reverse processes. The UV radiation dosage andintensity may be adjusted by those skilled in the art to achieve thedesired level of conversion, which may depend of film thickness andother factors. The UV radiation may be provided by any UV source, suchas mercury microwave arc lamps (e.g., H bulb, H+ bulb, D bulb, Q bulb,and V bulb type lamps), pulsed xenon flash lamps, high-efficiency UVlight emitting diode arrays, and UV lasers. Suitable optics may beemployed, if desired, to pattern the radiation or confine exposure onlyto desired areas. The UV radiation may have a wavelength between about170 nm and about 500 nm. A useful range of temperatures for thephotoreactions may be from about −25° C. to about 25° C.

In one embodiment, a cracked or otherwise structurally defectivephotoresponsive PHT polymer, such as that exemplified by the PHTmaterial containing resonance stabilized carbon-carbon double bondsproduced in reaction example 1, may be healed by irradiation with UVlight. This may be achieved by the formation of cyclobutane groups whichbridge the two opposing surfaces. The formation and propagation of acrack or fracture, inside a polymeric material or on its surface,involves breaking of chemical bonds or polymer chains. Self-healing orself-repair requires formation of new chemical bonds between the cracksurfaces, such as the formation of cyclobutane groups from the UVirradiation of a photoresponsive PHT containing resonance stabilizedcarbon-carbon double bonds. In a related embodiment, photoresponsivePHTs may contain pendant photoresponsive functionality or chemicalgroups. The pendant photoresponsive groups engage inphoto-polymerization or dimerisation reactions when irradiated with UVlight and may bridge or heal two opposing surfaces in a crack. It isexpected that pendant groups have greater degrees of rotational andtranslational freedom to engage in photodimerisation reactions and maythus be advantageous in terms of efficacy and photo-yield. Such pendantphotoresponsive groups may therefore provide enhanced “self-healing”properties for repairing cracks in PHT materials.

Reaction example 4 illustrates an alternate method for forming aphotoresponsive PHT that contains cyclobutane groups. Here, aphotoresponsive aminobenzene containing molecule or oligomer is producedprior to formation of a hexahydrotriazine containing polymer:

Reaction Example 4

The photoresponsive molecule or oligomer containing aminobenzene groupsand cyclobutane groups as shown is tetra-functional, and may be reactedto form photoresponsive PHT networks as shown in reaction example 5.

Reaction Example 5

The pathway to photoresponsive PHTs, as illustrated in reaction example5, may be advantageous because the cyclobutane groups are formed first,and the formation thereof does not depend on the proximity of tworesonance stabilized carbon-carbon double bonds, in contrast to thereaction pathway shown in reaction example 3, which involves thephotodimerisation or crosslinking of a polymer network with restrictedfreedom of movement and steric hindrance. It is suggested that thephotoresponsive PHT produced by reaction example 5 may provide greatercontrol over the degree of crosslinking or dimerisation, both in theforward and reverse directions, as the photoactive sites are preformed,and then integrated into the greater PHT polymer network afterpolymerization.

In addition to a [2π+2π] cycloaddition reactions used to createcrosslinks or cyclic carbon groups such as cyclobutane groups, [4π+4π]cycloaddition reactions may be used to create crosslinks or cycliccarbon groups other than cyclobutane groups. A useful group for such a[4π+4π] cycloaddition reaction is an anthracene polycyclic aromaticgroup, which may be used to create a crosslinks or cyclooctane groups(FIG. 1). In one embodiment, an anthracene diamine may be combined withparaformaldehyde per reaction example 1 to produce a photoresponsivepolymer containing anthracene groups. After UV irradiation at wavelengthof about 350 nm or greater, a new photoresponsive polymer containingcyclooctane groups may be produced.

The percent conversion of resonance stabilized carbon-carbon doublebonds to cyclobutane groups or the reverse photoreaction may bemonitored by techniques such as nuclear magnetic resonance spectroscopyand UV-visible spectroscopy techniques. In one embodiment, the percentconversion of carbon-carbon double bonds to form aliphatic cyclobutanegroups, or the reverse reaction, may be determined by UV-visiblespectroscopy, which may quantitatively detect differences between the UVabsorption characteristics of the starting resonance stabilized alkeneand the corresponding cyclobutane photoproduct, or the reverse reaction,to reform the carbon-carbon double bonds. For example, the electronicconjugation of resonance stabilized carbon-carbon double bonds, such asthat exemplified by molecules such as 4,4′-diaminostilbene, producesstrong UV absorption at certain wavelengths, such as those from about260 nm to about 300 nm, and as depicted by the “A” curve in FIG. 2.After dimerisation, or the formation of cyclobutane groups, conjugationis destroyed and the absorbance of the irradiated sample may be reducedsignificantly, as illustrated by curve “B” in FIG. 2. The reversereaction, involving cyclobutane cleavage, and the restoration ofconjugated bonds, is reflected in the increase of absorption from about270 nm to about 300 nm region, as shown by curve “C” in FIG. 2.Therefore, by monitoring changes in the UV absorbance at particularwavelengths, one may determine the extent of photodimerisation to formcyclic structures, or the reverse reaction, wherein conjugatedcarbon-carbon double bonds are restored.

In one embodiment of this disclosure, photoresponsive PHAs and PHTs maybe patterned using photolithography. Photolithography is a process usedin the electronics industry to create specific patterns or regions inphotoreactive materials (photoresists) in the production of electroniccomponents and integrated circuits. The photoresist may be a polymermaterial sensitive to a certain wavelength of electromagnetic radiation,and may be applied through a spin coating process. The photoresist maybe a carbon-based polymer sensitive to ultraviolet light, such as aphenolic resin matrix with a diazonapthoquinone sensitizer. Patterningof regions in a photoresist may be created by photolithographicprocesses as follows: a) layers of a photoresist material are coatedonto a substrate, such as a silicon wafer, and b), the photoresist layeris selectively exposed to a form of radiation, such as ultravioletlight, using an exposure tool and a patterned mask to effect the desiredexposure of certain areas defined by the photomask pattern, and c), thepatterns in the photoresist are formed when the photoresist isdeveloped, usually by the chemical action of a developer. In the casewhere the irradiated or exposed regions are developer soluble, apositive image of the mask is produced in the resist (positive resist).If the non-irradiated regions are dissolved by the developer, a negativeimage results (negative resist). Following development, the regions ofthe substrate no longer covered by photoresist may be removed by plasmaetching, thereby replicating the mask pattern in that substrate layer.

In a similar fashion, photoresponsive PHAs and PHTs may be used asphotoresists in the production of electronic articles such as passivecomponents and integrated circuits. As mentioned prior, a liquid PHAmaterial may be applied to an electronic article, patterned with UVlight, and then cured by heat treatment to produce a PHT material or amixture of PHA and PHT materials. Before or after heat curing, the filmmay be developed to form a patterned photoresponsive polymer disposedover an electronic article. FIGS. 3A-3C illustrate cross-sectional viewsrepresenting a photoresponsive PHT patterning process 300 according toone embodiment of this disclosure. As shown in FIG. 3A, aphotoresponsive PHT 301, disposed over and upon a substrate 302, isexposed to UV radiation from greater than 300 nm using a photomaskpattern according to known masking and patterning processes. FIG. 3Billustrates the pattern transferred to the photoresponsive PHT, whereinthe PHT film has unexposed areas 303 and UV radiation exposed areas 304.In one embodiment, the 304 areas may contain the reaction product(s) ofa [2π+2π] cycloaddition dimerisation reaction, wherein the reactionproducts contain cyclobutane group crosslinks. FIG. 3C illustrates thePHT patterned substrate after development with a strong acid, such ashydrochloric acid or sulfuric acid, wherein the unexposed PHT 303 may beremoved. The process used to remove the unexposed PHT 303 mayselectively etch PHT 303 at a greater rate than PHT 304, thusmaintaining the desired structural features of PHT 304. In otherembodiments, a patterning scheme may involve photo-cleavage ofcyclobutane groups and the restoration of the conjugated carbon-carbondouble bonds. A further advantage of the use of photoresponsive PHAs andPHTs in a photolithography process is that the photoresponsive polymerscontain photosensitive chemical groups integrated or bound to thepolymer structure, and thus do not require the addition of aphotosensitizer material, such as diazonapthoquinone to cause thephoto-response or initiate the photochemistry.

The terminology used herein is for the purpose of describing particularembodiments only and is not intended to be limiting of the invention. Asused herein, the singular forms “a”, “an” and “the” are intended toinclude the plural forms as well, unless the context clearly indicatesotherwise. It will be further understood that the terms “comprises”and/or “comprising,” when used in this specification, specify thepresence of stated features, integers, steps, operations, elements,and/or components, but do not preclude the presence or addition of oneor more other features, integers, steps, operations, elements,components, and/or groups thereof. When a range is used to express apossible value using two numerical limits X and Y (e.g., a concentrationof X ppm to Y ppm), unless otherwise stated the value can be X, Y, orany number between X and Y.

The description of the present invention has been presented for purposesof illustration and description, but is not intended to be exhaustive orlimited to the invention in the form disclosed. Many modifications andvariations will be apparent to those of ordinary skill in the artwithout departing from the scope and spirit of the invention. Theembodiments were chosen and described in order to best explain theprinciples of the invention and their practical application, and toenable others of ordinary skill in the art to understand the invention.

1. A method of patterning a substrate, comprising: forming a liquidpoly(hemiaminal) material by a process, comprising: forming a reactionmixture comprising a polar solvent, paraformaldehyde, and anaminobenzene compound comprising photoreactive groups; and heating thereaction mixture at a temperature up to 50° C.; applying the liquidpoly(hemiaminal) material to a substrate; patterning the liquidpoly(hemiaminal) material with UV light; and curing the liquidpoly(hemiaminal) material to form a cured poly(hexahydrotriazine)polymer.
 2. The method of claim 1, wherein patterning the liquidpoly(hemiaminal) material with UV light comprises exposing the liquidpoly(hemiaminal) material to the UV light through a mask.
 3. The methodof claim 2, wherein curing the liquid poly(hemiaminal) materialcomprises heating the liquid poly(hemiaminal) material.
 4. The method ofclaim 3, wherein the curing the liquid poly(hemiaminal) material to forma poly(hexahydrotriazine) polymer comprises heating the liquidpoly(hemiaminal) material to a temperature of from about 50° C. to about280° C. to form a cured poly(hexahydrotriazine) polymer.
 5. The methodof claim 3, wherein the curing the liquid poly(hemiaminal) material isperformed following the patterning the liquid poly(hemiaminal) material.6. The method of claim 1, wherein the aminobenzene compound comprises atleast two amine groups.
 7. The method of claim 1, wherein thephotoreactive groups comprise at least one of a carbon-carbon doublebond or a cyclic carbon group.
 8. The method of claim 1, wherein thephotoreactive groups comprise a reaction product of a [2π+2π]cycloaddition reaction, a reverse [2π+2π] cycloaddition reaction, a[4π+4π] cycloaddition reaction, a reverse [4π+4π] cycloadditionreaction, or a combination thereof.
 9. The method of claim 1, furthercomprising treating the cured poly(hexahydrotriazine) polymer with astrong acid.
 10. A method of patterning a substrate, comprising: forminga liquid poly(hemiaminal) material by a process, comprising: forming areaction mixture comprising a polar solvent, paraformaldehyde, and anaminobenzene compound comprising photoreactive groups and at least twoamine groups; and heating the reaction mixture at a temperature up to50° C.; applying the liquid poly(hemiaminal) material to a substrate;patterning the liquid poly(hemiaminal) material with UV light; andcuring the liquid poly(hemiaminal) material to form a curedpoly(hexahydrotriazine) polymer.
 11. The method of claim 10, whereinpatterning the liquid poly(hemiaminal) material with UV light comprisesexposing the liquid poly(hemiaminal) material to the UV light through amask.
 12. The method of claim 10, wherein curing the liquidpoly(hemiaminal) material comprises heating the liquid poly(hemiaminal)material.
 13. The method of claim 12, wherein the curing the liquidpoly(hemiaminal) material to form a poly(hexahydrotriazine) polymercomprises heating the liquid poly(hemiaminal) material to a temperatureof from about 50° C. to about 280° C. to form a curedpoly(hexahydrotriazine) polymer.
 14. The method of claim 12, wherein thecuring the liquid poly(hemiaminal) material is performed following thepatterning the liquid poly(hemiaminal) material.
 15. The method of claim10, wherein the photoreactive groups comprise at least one of acarbon-carbon double bond or a cyclic carbon group.
 16. The method ofclaim 10, wherein the photoreactive groups comprise a reaction productof a [2π+2π] cycloaddition reaction, a reverse [2π+2π] cycloadditionreaction, a [4π+4π] cycloaddition reaction, a reverse [4π+4π]cycloaddition reaction, or a combination thereof.
 17. The method ofclaim 10, further comprising treating the cured poly(hexahydrotriazine)polymer with a strong acid.
 18. A method of patterning a substrate,comprising: forming a liquid poly(hemiaminal) material by a process,comprising: forming a reaction mixture comprising a polar solvent,paraformaldehyde, and an aminobenzene compound comprising photoreactivegroups, the photoreactive group comprising a reaction product of a[2π+2π] cycloaddition reaction, a reverse [2π+2π] cycloadditionreaction, a [4π+4π] cycloaddition reaction, a reverse [4π+4π]cycloaddition reaction, or a combination thereof; and heating thereaction mixture at a temperature up to 50° C.; applying the liquidpoly(hemiaminal) material to a substrate; patterning the liquidpoly(hemiaminal) material with UV light; and curing the liquidpoly(hemiaminal) material to form a cured poly(hexahydrotriazine)polymer.
 19. The method of claim 18, wherein patterning the liquidpoly(hemiaminal) material with UV light comprises exposing the liquidpoly(hemiaminal) material to the UV light through a mask, and whereinthe curing the liquid poly(hemiaminal) material to form apoly(hexahydrotriazine) polymer comprises heating the liquidpoly(hemiaminal) material to a temperature of from about 50° C. to about280° C. to form a cured poly(hexahydrotriazine) polymer.
 20. The methodof claim 18, wherein the photoreactive groups are selected from thegroup consisting of anthracenes, cinnamic acids, coumarins, thymines,stilbenes, and a combination thereof.